IWebBrowser2: how to force links to open in new wi

问题:

The MSDN documentation on WebBrowser Customization explains how to prevent new windows from being opened and how to cancel navigation. In my case, my application is hosting an IWebBrowser2 but I don't want the user to navigate to new pages within my app. Instead, I'd like to open all links in a new IE window. The desired behavior is: user clicks a link, and a new window opens with that URL.

A similar question was asked and answered here and rather than pollute that answered post, it was suggested I open a new discussion.

The members on the related post suggested I should be able to do this by trapping DISPID_BEFORENAVIGATE2, setting the cancel flag, and writing code to open a new window, but I've found out that the browser control gets lots of BeforeNavigate2 events that seem to be initiated by scripts on the main page. For example, amazon.com fires BeforeNavigate2 events like crazy, and they are not a result of link invocation.

Replies appreciated!

回答1:

Sorry to answer my own question here, but in the hopes that this may help somebody else, what I ended up doing was using IHTMLDocument directly rather than IWebBrowser. IWebBrowser is a superset of IHTMLDocument, and the navigation model implemented by IWebBrowser isn't customizable to the degree I wanted.

I actually got MS Developer Support involved and this approach was their recommendation. They say this is what Outlook uses for HTML-based email, which is the user experience I wanted to emulate. They also confirmed that there's no reliable way to filter the OnBeforeNavigate events that result from user action from those that result from script activity.

Hope this helps anybody facing the same issues. It wasn't too hard to port the code to use IHTMLDocument. If you end up doing this, you may also find yourself looking for a way to figure out when the document is done loading. To do that, hook HTMLDocumentEvents instead of DWebBrowserEvents, and look for the DISPID_HTMLDOCUMENTEVENTS_ONREADYSTATECHANGE event. It doesn't tell you what the ready state is; you need to call IHTMLDocument::get_readyState and parse the resulting string. Goofy, but there you go.

回答2:

I'm hypothesising here but yet another approach could be to maintain a count of navigation events, incrementing the counter on DISPID_BEFORENAVIGATE2 and decrementing it on occurrences of DISPID_NAVIGATECOMPLETE2 and DISPID_NAVIGATEERROR. With that in place, you could speculate that whenever you get DISPID_BEFORENAVIGATE2 and your counter is at zero, it is actual user navigation / link invocation.

I have no idea whether this approach would work, or whether those are the right events you'd need to make it work, but it could be worth investigating.

回答3:

You could try a different approach instead and physically add the attribute target="_blank" to all <a> tags in the rendered document.

This approach would involve waiting for DISPID_DOCUMENTCOMPLETE and then using IHTMLDocument3::getElementsByTagName() to fetch all of the anchor elements. You would then use IHTMLElement::setAttribute() to set target="_blank" on each of them.

回答4:

It seems to me, that it you want "to open all links in a new IE window", it means that you want that the opening of new windows must be done in another process. The easiest way to do so: using CreateObject("InternetExplorer.Application") way (see another question which solve a problem, which is opposite to your question: InternetExplorer.Application object and cookie container). With this way you will receive the best isolation from your application and the user who clicks on the link receive all possibilities which exist in IE. You should of cause continue usage of BeforeNavigate2 events to find out the moment when "a new IE window" should be opened.

回答5:

You can bind to onclick event before document is complete while creating browser in OnCreate() using IHTMLDocument2::put_onclick():

#include <comutil.h>

ClickEvents<RootFrame> clickEvents;
_variant_t clickDispatch;
clickDispatch.vt = VT_DISPATCH;
clickDispatch.pdispVal = &clickEvents;

CComQIPtr<IDispatch> dispatch;
hr = webBrowser2->get_Document(&dispatch);
ASSERT_EXIT(SUCCEEDED(hr), "webBrowser->get_Document(&dispatch)");

CComQIPtr<IHTMLDocument2> htmlDocument2;
hr = dispatch->QueryInterface(IID_IHTMLDocument2, (void**) &htmlDocument2);
ASSERT_EXIT(SUCCEEDED(hr), "dispatch->QueryInterface(&htmlDocument2)");

htmlDocument2->put_onclick(clickDispatch);

ClickEvents class implements IDispatch, you only need to implement Invoke method, in rest return E_NOTIMPL:

HRESULT STDMETHODCALLTYPE Invoke(DISPID dispIdMember, REFIID riid, LCID lcid, WORD wFlags,
    DISPPARAMS *pDispParams, VARIANT *pVarResult, EXCEPINFO *pExcepInfo, UINT *puArgErr)
{
    HRESULT hr;

    CComQIPtr<IWebBrowser2> webBrowser2;
    hr = rootFrame->GetDlgControl(rootFrame->rootview.GetDlgCtrlID(), IID_IWebBrowser2, (void**) &webBrowser2);
    ASSERT_EXIT(SUCCEEDED(hr), "rootframe->GetDlgControl(IID_IWebBrowser2) failed");

    CComQIPtr<IDispatch> dispatch;
    hr = webBrowser2->get_Document(&dispatch);
    ASSERT_EXIT(SUCCEEDED(hr), "webBrowser2->get_Document(&dispatch)");

    CComQIPtr<IHTMLDocument2> htmlDocument2;
    hr = dispatch->QueryInterface(IID_IHTMLDocument2, (void**) &htmlDocument2);
    ASSERT_EXIT(SUCCEEDED(hr), "dispatch->QueryInterface(&htmlDocument2)");

    CComQIPtr<IHTMLWindow2> htmlWindow2;
    hr = htmlDocument2->get_parentWindow((IHTMLWindow2**) &htmlWindow2);
    ASSERT_EXIT(SUCCEEDED(hr), "htmlDocument2->get_parentWindow(&htmlWindow2)");

    CComQIPtr<IHTMLEventObj> htmlEvent;
    hr = htmlWindow2->get_event(&htmlEvent);
    ASSERT_EXIT(SUCCEEDED(hr), "htmlWindow2->get_event(&htmlEvent)");

    CComQIPtr<IHTMLElement> htmlElement;
    hr = htmlEvent->get_srcElement(&htmlElement);
    ASSERT_EXIT(SUCCEEDED(hr), "htmlEvent->get_srcElement(&htmlElement)");

    CComBSTR hrefAttr(L"href");
    VARIANT attrValue;
    VariantInit(&attrValue);
    hr = htmlElement->getAttribute(hrefAttr, 0 | 2, &attrValue); // 0 = case insensitive, 2 = return BSTR
    ASSERT_EXIT(SUCCEEDED(hr), "htmlElement->getAttribute()");

    wchar_t href[2084]; // maximum url length in IE, http://support.microsoft.com/kb/208427
    wcsncpy_s(href, _countof(href), attrValue.bstrVal, _TRUNCATE);

    if (!rootFrame->IsURLAllowed(href)) {

        VARIANT variant;
        variant.vt = VT_BOOL;
        variant.boolVal = VARIANT_FALSE;
        htmlEvent->put_returnValue(variant);

        ShellExecute(0, L"open", href, 0, 0, SW_SHOWNORMAL);
    }

    return S_OK;
}

As you can see after querying some interfaces I finally have the element that got clicked, then I call IsURLAllowed() defined in my root frame to check whether to allow opening url in current webbrowser window or whether to open it using default browser on user's computer.

This handles all links even if they were appended to document using javascript.

The same should be done with "onsubmit" events for forms.

I also think I have a solution for "window.location" redirects in javascript, I haven't tested it yet, but I will soon test it and I will update this answer then. You could use a combination of "onunload" and "onbeforeunload" events along with DWebBrowserEvents2::BeforeNavigate2(), after onunload/onbeforeunload are called you will know that user is leaving current page so now in BeforeNavigate2() you can cancel it. You can attach unload events using IHTMLWindow2::put_onunload() and IHTMLWindow2::put_onbeforeunload().

See sources of a complete solution for the "onclick" below.

AttachClickEvents in BrowserFrame:

http://code.google.com/p/phpdesktop/source/browse/phpdesktop-msie/msie/browser_frame.h?r=709d00b991b5#125

Invoke in ClickEvents(IDispatch):

http://code.google.com/p/phpdesktop/source/browse/phpdesktop-msie/msie/click_events.h?r=a5b0b350c933#132